Means for adjusting the effective length of bribge-cottntekbhaces



No. 8,224. A PATENTED JULY .15, 1851. D. o. MEGALLUM. MEANS EOEADJUSTING TEE EFFECTIVE LENGTE -O'EBEIDGE COUNTER BEAGES.

N STATES 4Farm.TT OFFICE.- N

. D. `o. MeoALLUM, or owiaeo, New ronK.

` "MEANS For. ADJUSTING THE AEFrnctrivr. LENGTH oF Baines-CONTERBRAQES.i

. spcification of Letters Patent naseaeatea Juiy 15, 1851.

companying drawings, forming partfof this' t specification, in which*H"F'gure, l is 1alongitudinal elevation of a bridge girder. Fig. 2 is alongitudinal vertical section of part of `the same. t Sis a plan of partof the upper chord." Fig. i this `a transverseisection through theline@fain Fig. 1f, i. Figs.`5 and 6 represent the counter braces,` ona`scale larger than the othergu-rfes.

` Sfn-filarletters ofreference indicate cort respondingparts in each ofthe several `figures; p i

'My inventionrelates to the construction of open built beamsor girdersemployed in bridges, and `other structures of asimilar nature.

My `improvement consists in a new method of lengthening, orshorteningthecounter braces, whereby I enabled to produce and maintainany required down- `ward vertical strain, or deflection, upon thegirders, and which method I deem far more useful in practice than thosesometimes employed of using gibs and keys, or wedges for that purpose.

A, represents the lower chord of the girder, composed of four dr of anysuitable number of string pieces bolted together and having cleats a, a,placed between them at suitable distances. -having only a very slightcamber.

It is nearly straight, B, is the upper chord, formed also of anysuitable number offstringers, and is of an arched form. The two `chordsare connected by posts 0,0, forming' radii to the upper chord,

and` also at'their ends, by vertical` posts E, E, all of the said postsbeing so connected with the chords as to maintain the required positionsof the several parts.

D, D, are thrust braces, each notched into the top of one oi the postsC, C, and into the foot of the next post nearer the end of the girder.

F, F, are inclined ties, or tension rods, outside the girder. t

G, G, are ties, or tension rods, similar to Fig.

F, F, passing through the lower and upper chords of the girder, at aboutthe middleof its thickness.

Theseveral parts of thegirder, as far as I have described them, do notdiffer, essentially, in their `construction and arrangement from thoseof some other girders ,in use. Each of the` ties or tension rods lastdescribed, G, is incased by a counter brace H, the lowerpartfof which isof wood, and may be eitherf in one piece, bored through, t admit theArod, 4"or in two pieces, placed one on y.each side of the rod; the lowerend abutting on `a step b, placed on the lower chord,

t at the foot of the posts @,and its upper end `fitted to a metallicsheath I, through which also` the tensionrod passes. Thissheath, whichlis best shown in Figs. 15 and 6consists of a `tubejhaving at its lowerend `a socketlinto which the top of the counter braceH,`is fitted. Thetension rodspass through clamping pieces c, J0, under the lower chord,and others c', 0", above `the upper chord.` These clamping pieces bearalso against the head and foot of the posts C, C. `Theupper end of thesheath passes through the clamping piece c', .andis of suflicient lengthto project a shortudistance above it. `A plate of metal, ,having 4a holethrough it of justsuliicient size topass the rod G is attached, at thetop of thel girder, by bolts e, e, which pass through the clampingpieces, the upper chord, and the posts C, C, in a direction parallelwith the tension rods. This plate bears` on `top of the sheath I.

J, is an arched beam, placed immediately i below the upper chord B, andnotched between the posts C, C. IteXtends: from the crown of the arch`about half way tothe` pass through the lower chord A, and thebolstersI1, L, and rest in seats, on the top of the abutments or piers.

M, M, are other inclined struts their upper ends abuttingagainst stepsg, g, under the upper chord B. They are secured to the posts, and passthrough the lower chord and bolsters, and rest upon the abutments orpiers, in a similar manner to K, K. Those counter braces H H which comein the way put together, and all except the tension rods G, G, andbolts, e, e, are bolted or screwed up. The bridge should then be loadedwith a weight, greater than it will ever be required to bear, inordinary traflic. It has been stated, in the foregoing description, thatthe length ofthe counter braces, is such, as to allow the ends of themetallic sheaths I, I, to project through the clamping pieces,

c', 0. This projection should be such, that the deflection of thegirders, caused by the weight on the bridge, will, by increasing thedist-ance between the steps b, b, and the clamping pieces 0, c', causethe ends of the sheaths, to stand exactly flush, or a little above, theface of the clamping pieces. The plates, d, d, are then screwed down, tobear on the end of the sheaths, by means of the nuts and the bolts e, e,by which the deflection, producedby the load is maintained, after theload shall have been removed. The nuts on the ties or tension rods-G, G,may then be screwed up, to bring t-he required degree of tension uponthem.V

The braces H, H might be continued through the upper chord of thegirder, but

the metallic sheath I, is better suited, as it deflection, may bebrought upon it, without increasing Jthe strain, or deflection, andconsequently the girder will not be subjected to any vertical vibration,by the passing of this lesser weight over it. Wedges have been used, toeffect this desirable object, but as they are liable to become loose,and work out of place, an effectual remedy and substitute is abovedescribed. 0

lVhat I claim as my invention, and desire to secure by Letters Patent,is y The method of lengthening or shortening the counter braces of agirder or bridge truss, so as to produce and maintain any desired,vertical strain, or deliection, of the girder or truss by means of thecounter brace H, Whether all of'wood or provided with a metallic end orsheath; the plate of metal ci, bearing, upon the metallic end or sheath,(or upon the end of the wood, when the metallic end or sheath is notused) Y at the top of the girder; and the nuts, and the bolts e, e,passing through the clamping pieces, c, c, the upper chord, and theposts, by which the plate of metal d, is drawn down upon the metallicend or sheath and the adjustment ofthe length, of the counter brace iseffected, substantially as herein described.

D. C. MCGALLUM.

lVitnesses:

W. H. STEWART, SILAs C. HAY.

